London attack: Police ‘keeping open mind’ about more Tube bombing suspects after ‘very significant arrest’

Security officials fear the prospect of a wider terrorist cell

Police are keeping an 'open mind' over the possibility of more suspects (AFP)

Police are keeping an “open mind” over whether more than one suspect was involved in the Parsons Green bombing, Deputy Assistant Commissioner Neil Basu has said.

An 18-year-old was detained in Dover earlier on Saturday, in what Mr Basu described as a "very significant" arrest.

But Mr Basu said the terror threat level would remain at "Critical" - the highest level - while officers investigated whether others were involved.

He said: "At this stage we are keeping an open mind over whether more than one person is responsible for the attack and we are still pursuing numerous lines of inquiry and at great pace."

Echoing similar comments from the Home Secretary, Amber Rudd, Mr Basu added: "All I am prepared to say at the moment is it is a very significant arrest, but as I said we are open-minded.

"If there are other people responsible it's our job to find them and that is part of the reason that we are remaining at critical threat."

It is unknown whether the person who left a bomb on the London Underground was part of a larger cell.

A house in Surrey has been raided by officers as part of the investigation. Local residents said they were given one minute to evacuate the area.

Thirty people were treated for injuries sustained in the blast, Mr Basu confirmed.

The attack, which used an improvised explosive device (IED), was claimed by extremist group Isis.

The IED failed to detonate properly but investigators have found traces of triacetone triperoxide (TATP), known as the “mother of Satan”.

The chemical has been used by Isis before, including in attacks in Manchester, Paris and Brussels.

More recently, traces of TATP were found in a terrorist safe house in Alcanar, Spain. It is believed the highly unstable substance blew up accidentally.

Here is the full statement from Mr Basu delivered at around 7pm on Saturday evening

“I would like to update you on the ongoing investigation into the terrorist attack at Parsons Green Tube Station yesterday morning.

“The Metropolitan Police and its partners across the Counter Terrorism Policing Network have been working around the clock and through the night to identify, locate and arrest those responsible for this cowardly crime.

“At approximately 7.50am this morning, local police officers in Kent arrested an 18-year-old man in the departure area of the Port of Dover. He was arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism. He has now been transferred to custody at a police station in London.

“Officers from Kent Police partially evacuated the Port of Dover at around 11.40am this morning. This was to enable them to search the premises as a precautionary measure. This work is now complete. They recovered a number of items during this search.

“A short while later, at around 1.40pm - with the assistance of Surrey Police - Met Police officers also evacuated a house in Sunbury-on-Thames. As a precautionary measure, we evacuated the surrounding buildings and set up cordons within a 100-metre radius.

“I want to reassure that community that our expert officers are quickly and thoroughly searching that address and working to ensure that it is safe. Once this is done a detailed search will take place.

“I would like to thank residents in Sunbury and people travelling in and out of the Port of Dover for their patience and understanding while officers carry out this precautionary but important work.

“Their support has enabled us to act swiftly.

“The police and Surrey Local Authority are working to support displaced residents and to get them back into their homes as soon as possible.

“At this stage we are keeping an open mind around whether more than one person is responsible for the attack and we are still pursuing numerous lines of enquiry and at a great pace.

“So what happens next? Our priorities are to ensure that the address in Sunbury is safe and to identify and locate any other potential suspects.

“We have identified 121 witnesses so far, and we have spoken to 100 of them already. Officers continue to trawl through many hours of closed circuit television footage and more than 180 videos and pictures that have been sent to them by the public. We continue to take large numbers of calls from the public via the confidential Anti Terrorist Hotline.

“The public’s help remains crucial, and I urge anyone with information, no matter how significant they think it is, to continue letting us know.

“Police officers across the UK are also still out in force, protecting communities.

“Yesterday the Prime Minister announced that the terrorism threat level had been raised to critical by the independent Joint Terrorism Analysis Centre, or JTAC. This means a terrorist attack is not only highly likely but a further attack may be imminent. The threat level remains at critical for the time being but is under constant review.

“Military personnel have been drafted in to protect national infrastructure sites, allowing additional armed police officers to carry out patrols. And we are very grateful for our military colleagues’ support.

“Communities across the UK will continue to see more officers, both armed and unarmed, on patrol by foot and in vehicles over the remainder of the weekend. In particular, they will be patrolling at crowded places, iconic sites, transport hubs and ports.

“In total, we know that 30 people have received treatment at hospital for injuries. We are incredibly grateful that no one was killed yesterday but my thoughts are with those people and everyone affected by this terrible and traumatic attack.

“I would like to finish by thanking the public for their support at this crucial time.

“The fact that so many communities stand together against the cowardice that is terrorism is a tremendous strength here in the UK.”